Abstract: Methods and apparatus are provided for authenticating a remote service to another service on behalf of a user. A user client authorizes a remote application client to perform one or more actions with a server on behalf of the user client. The user client provides one or more keys to a remote authentication service; receives an identifier of the remote application client, where the remote authentication client is remote from the server; and notifies the remote authentication service that the remote application client is authorized to obtain a response from the remote authentication service regarding a challenge from the server, where the response is based on at least one of the one or more keys stored by the remote authentication service on behalf of the user client.